Abstract
Photoacoustic (PA) imaging is able to provide extremely high molecular contrast while maintaining the superior imaging depth of ultrasound (US) imaging. Conventional microscopic PA imaging has limited access to deeper tissue due to strong light scattering and attenuation. Endoscopic PA technology enables direct delivery of excitation light into the interior of a hollow organ or cavity of the body for functional and molecular PA imaging of target tissue. Various endoscopic PA probes have been developed for different applications, including the intravascular imaging of lipids in atherosclerotic plaque and endoscopic imaging of colon cancer. In this paper, the authors review representative probe configurations and corresponding preclinical applications. In addition, the potential challenges and future directions of endoscopic PA imaging are discussed.
Highlights
To access comprehensive structural and functional information of internal organs, various imaging technologies, such as optical coherence tomography (OCT), ultrasound (US), and near infrared fluorescence (NIRF) imaging have been developed for endoscopic imaging and used in clinical applications
Apart from the above conventional piezoelectric materials and their composites, new materials and technologies are emerging in PA/US endoscopy, including lead free piezoelectric materials [80], micromachine based US transducers [81,82,83,84,85,86], and optical based acoustic
Apart from the above conventional piezoelectric materials and their composites, new materials and technologies are emerging in PA/US endoscopy, including lead free piezo10 of 21 electric materials [80], micromachine based US transducers [81,82,83,84,85,86], and optical based acoustic sensing [87]
Summary
To access comprehensive structural and functional information of internal organs, various imaging technologies, such as optical coherence tomography (OCT), ultrasound (US), and near infrared fluorescence (NIRF) imaging have been developed for endoscopic imaging and used in clinical applications. A portion of the optical energy is absorbed by tissue tage of providing optical absorption contrast with a greater penetration depth compared and converted into heat, resulting in a transient pressure rise. This initial pressure acts as with conventional optical imaging modalities [4,5,6,7,8,9,10,11,12]. Studies have reported that ICG is able to target lipid loaded macrophages, which can be Photonics 2021, 8, x FOR PEER REVIEW enhance the PA signal or provide additional optical contrast. Different probe designs and further summarize a representative PA imaging system with key parameters of performance
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